Field of the Invention
The present invention relates to a reducing agent injection device, an exhaust gas treatment device, and an exhaust gas treatment method. More specifically, the present invention relates to the reducing agent injection device that can generate and inject ammonia from a urea solution with less energy. Further, the present invention relates to the exhaust gas treatment device that includes this reducing agent injection device, and that can treat NOx in an exhaust gas with less energy even when the exhaust gas is at low temperature. Furthermore, the present invention relates to the exhaust gas treatment method that can treat NOx in the exhaust gas with less energy by use of this exhaust gas treatment device, even when the exhaust gas is at low temperature.
Description of Related Art
Conventionally, a selective catalytic reduction type NOx catalyst (an SCR catalyst) has been used to purify nitrogen oxides (NOx) in the exhaust gas discharged from various kinds of engines and the like (for example, see Patent Documents 1 to 3).
The exhaust gas purifying device disclosed in Patent Document 1 has a catalyst (an SCR catalyst) mounted on an exhaust pipe of an engine and means for injecting a urea water into the exhaust pipe between the engine and the catalyst. Further, in the exhaust gas purifying device, a plurality of urea water injection means, which mixes the urea water and the exhaust gas, and mixes the urea water with the exhaust gas while causing the urea water to react with a specific component in the exhaust gas by the catalyst, are provided in a plurality of places.
The device disclosed in Patent Document 2 is the device for reducing nitrogen oxides in the exhaust gas in an internal combustion engine. Further, the device includes a thermal decomposition reactor to generate ammonia from a solid urea, a heating device, and an SCR catalyst, and cause the ammonia generated from the solid urea to flow in the SCR catalyst.
The device disclosed in Patent Document 3 is the device for evaporating at least one of a reducing agent precursor (urea) solution and a reducing agent precursor (urea). The evaporated substance (urea) is to undergo hydrolysis by a hydrolysis catalytic converter arranged on a downstream side. This device includes a heating zone and a heating element arranged in the heating zone, and evaporates at least one of the reducing agent precursor solution and the reducing agent precursor by the heating element. The hydrolyzed substance (ammonia) by the hydrolysis catalytic converter is used for a reduction treatment in the SCR catalytic converter.